The Senate Commerce Committee report says Target missed multiple warning signs that intruders had broken into company networks and were stealing millions of credit and debit card numbers and other sensitive customer information.

The giant retailer hired a vendor that didn't follow commonly-accepted security practices and then ignored warnings that hackers were installing malicious software on the point of sale terminals, according to the report.

John Mulligan, Target's chief financial officer, likely will face tough questions about his company's response on Wednesday when he testifies before the Commerce Committee, which includes Sen. Amy Klobuchar. Mulligan testified last month in front of the Senate Judiciary Committee about the data breach.

The Senate is working on legislation to tighten the protection of consumer data.